This invention relates generally to a belt drive two speed shift mechanism for a rotatably driven device such as a crop residue chopper of an agricultural combine, and more particularly, to a belt drive shift mechanism which allows conveniently and easily manually shifting between two drive ratios by moving a shift collar between a position engaged with a first pulley to be driven by a belt at one rotational speed, and a second pulley to be driven by a belt at another speed.
Commonly, it is desired to have the capability to change the speed of rotation of belt driven items on agricultural combines, such as crop residue choppers and the like. Typically to accomplish this, a tensioning mechanism for the belt or belts must be disengaged or released. The belt or belts must then be moved from one set of pulleys to a second set of pulleys. Then, the belt tension mechanism must be re-engaged. Belt tension on such drives is typically relatively high and thus a mechanical advantage device, such as a relatively long lever arm, is utilized to engage and disengage the tension mechanism. Moving the belt or belts can be difficult due to the length of the belts, and/or the location thereof.
Thus, what is sought is a belt drive shift mechanism for rotatable items on agricultural machines such as combines and the like, which eliminates the need for engaging and disengaging the belt tension mechanism, and physically moving the belt or belts from one set of pulleys to another.
According to the present invention, a two speed shift mechanism for a belt drive which provides many of the above sought properties, is disclosed. The present mechanism includes a rotatable shaft including a first pulley mounted thereon for rotation therewith, a tube concentric with the shaft and rotatable therearound, the tube including a shift hub mounted around a portion thereof for rotation therewith, and the shift hub supporting a second pulley in axially spaced relation to the first pulley for concentric rotation about the shift hub. The mechanism includes a shift collar mounted around the shift hub in the space between the first pulley and the second pulley for rotation with the shift hub and for axial movement relative thereto between a first position adjacent the first pulley and a second position adjacent the second pulley. The collar and the first pulley include elements cooperatively engageable when the collar is in the first position for connecting the collar to the first pulley for rotation of the collar, the shift hub and the tube therewith, and the collar and the second pulley include elements cooperatively engageable when the collar is in the second position for connecting the collar to the second pulley for rotation of the collar, the shift hub, and the tube therewith, the mechanism further optionally including a releasable element for holding the collar in the first and second positions, respectively.
To selectably shift from one belt drive to the other, the collar is simply an easily released and moved to the position for engaging the other belt and locked in position. No physical movement of the belts is required, nor is releasing and re-engaging a tensioner.